Jordan block size

I was wondering about the size of the Jordan blocks of the following matrix.

$$\begin{bmatrix} 0 & 1 & 0\\ 0 & 0 & 1\\ 0 & 0 & 0 \end{bmatrix}$$

I know that Jordan blocks have $1$'s on the superdiagonal. So are these $3$ blocks of size $1 \times 1$ or is this one block of size $3 \times 3$? I'm not sure how to tell the difference. Thanks in advance.